This invention relates generally to servo seeking and tracking systems for use in computer disk drive units and the like. More specifically, this invention relates to an improved servo seeking and tracking system wherein unique track address information is prerecorded onto a dedicated servo surface and monitored during operation of the disk drive unit to identify and correct seeking and tracking errors.
In recent years, microcomputer equipment particularly such as so-called personal and desk top computers have become extremely popular for a wide variety of business and educational and other uses. Such computers commonly include a main central processor unit having one or more memory storage disks for storage of data. In many modern computers, the storage disk or disks, sometimes referred to as "hard disks," are provided as part of a Winchester-type disk drive unit having the storage disks supported in a stack on a rotary spindle within a substantially sealed disk drive housing. The disks are rotatably driven in unison by a small spindle motor within the disk drive housing, and one or more electromagnetic heads are displaced by a head positioner assembly to traverse surfaces of the rotating disks for purposes of reading and writing data. Such Winchester-type disk drive units are generally preferred in comparison with so-called floppy disk drives due to their higher memory storage capacities and faster operating speeds.
For a typical Winchester-type disk drive, data is recorded onto magnetizable surfaces or surface films on the memory storage disks in the form of data bits adapted to be encoded and decoded in binary form. The data is recorded within the confines of narrow concentric tracks defined on the disk surfaces, with track densities in the range of 500 to 1,000 and more tracks per inch being relatively well known. Accordingly, the total memory storage capacity for any selected disk drive unit is directly proportional to the number of available of data tracks. When the disk drive unit includes multiple storage disks, the total number of available data tracks and thus the total memory storage capacity is increased.
In normal operation of a Winchester-type disk drive unit, a system controller is provided for identifying the location of data which has been recorded upon the storage disks, typically through the use of directory name, file name, and/or data address information. When reading of specific data track is desired, the system controller signals a head positioner assembly to displace the heads to the desired position accessing the data. Alternately, when data recording or writing is desired, the system controller signals disk drive circuitry to command the positioner assembly to displace the heads in a manner aligning one head with a vacant data track. Importantly, for accurate track seeking and head alignment therewith, detectable servo information is normally prerecorded onto one or more of the memory storage disks.
In accordance with one known servo seeking and tracking system, each surface of each disk includes servo information prerecorded within radially spaced servo segments or sectors. This type of servo system, commonly known as an "embedded" servo system, provides data which is read by the operating head for purposes of seeking and tracking with a designated data track. During head traverses to seek a new specified data track, the head responds to embedded track address information within the servo sectors to identify a specified destination track. While such embedded servo systems have functioned generally satisfactorily, such systems inherently include track seek or access speed limitations due primarily to the limited sample rate at which the head can read and respond to servo information within the servo sectors. This inherent seek speed limitation is rendered more significant when relatively high track densities are used. Moreover, an embedded servo system fixes the number of available data and servo sectors in a manner which is incompatible with some types of controller interfaces.
So-called "dedicated" servo surface systems are also generally known in the art, wherein servo seeking and tracking information is prerecorded onto one surface of a memory storage disk in a disk drive unit having multiple disks. The servo seeking and tracking information is detected by an associated servo head for purposes of displacing and aligning a group of data heads with a designated data track, or to identify track crossings during a seek/access step. Such dedicated servo surface systems are preferred in certain multiple disk microcomputer applications since they can provide an overall increased data storage capacity to the disk drive unit. However, similar to the embedded servo systems described above, track seek/access errors can arise as a result of small disk imperfections which can generate false track crossing readings. Moreover, to prevent head overshoot during a seek step, head deceleration at the conclusion of the seek step must normally be designed for a relatively slow, worst case condition.
There exists, therefore, a significant need for an improved servo seek/tracking and related track address system for use in computer disk drive units, wherein the system is relatively simple and operates automatically to prevent and/or correct track seek and head positioning errors. The present invention fulfills these needs and provides further related advantages.